Leaching chambers made from thermoplastic materials are well known in the art and are widely used for receiving and dispersing wastewater, typically from a septic tank, into soil and other media. Such chambers typically have an arch shaped cross section defining a concave interior cavity having an open bottom, perforated sidewalls and a multiplicity of corrugations. Generally, these chambers store substantial quantities of wastewater within their concave interior cavity, thus provide a leaching area for dispersal of the wastewater by means of the chamber open bottom and perforations in the sidewalls. In fact, one of the performance objectives of the chambers is to provide an interior cavity that is large in order to contain as much wastewater as possible. The larger the interior cavity of the chamber is, the more wastewater that can be stored and dispersed into the surrounding soil.
Because these chambers are buried under soil, they need to have sufficient strength to support the overlying soil as well as other loads, such as motor vehicles which traverse the soil surface or other weighted objects that may be placed on the soil surface in proximity to the chamber. Accordingly, these chambers are typically designed to include certain physical characteristics that allow them to have the requisite strength while meeting certain performance objectives. These physical characteristics include wall (material) thickness, arch shaped cross section, corrugations and support pillars which extend downwardly into the interior cavity. However, one of the performance objectives is to allow one chamber to nest on top of a like chamber with a stack height that is within an acceptable range. This is because stack heights that are too high make the storage and transport of nested chambers less efficient because fewer chambers can be stacked within a given volume. Accordingly, in order for the chambers to be both nestable and include support pillars, the support pillars were made to have a hollow cavity. As such, when a first chamber is stacked on top of a like second chamber, the support pillars of the first chamber would be contained within the hollow cavity of the pillars of the like second chamber.
Unfortunately however, as the chambers are buried under overlying soil, the overlying soil enters and fills up the hollow cavity of the downward extending support pillars. This is undesirable because the presence of the support pillars filled with soil cause the available volume of the interior cavity of the chamber to be substantially reduced, thereby reducing the volume of wastewater that the chamber can contain and disperse.